Staircase



FIG. 1 is a perspective view of a staircase in accordance with the present design. The staircase has a transparent character.

FIG. 2 is a front view for the staircase shown in FIG. 1.

FIG. 3 is a rear view for the staircase shown in FIG. 1.

FIG. 4 is a left side view for the staircase shown in FIG. 1.

FIG. 5 is a right side view for the staircase shown in FIG. 1.

FIG. 6 is a top view for the staircase shown in FIG. 1; and,

FIG. 7 is a bottom view for the staircase shown in FIG. 1. 

We claim the ornamental design for a staircase, substantially as shown and described. 